1. Field of the Invention
The present invention relates generally to a mobile communication terminal, and in particular, to a reception diversity apparatus and method for the mobile communication terminal.
2. Description of the Related Art
A mobile communication terminal, such as a CDMA (Code Division Multiple Access) cellular/PCS (Personal Communications Service) mobile terminal, a hand-held phone or an IMT-2000 (International Mobile Telecommunication 2000) terminal, transmits and receives information using an RF (Radio Frequency) signal. In particular, an advanced mobile communication terminal is equipped with a GPS (Global Positioning System) receiver for receiving, from a GPS satellite, absolute-time information necessary for worldwide time synchronization and position information necessary for calculating latitude/longitude. In addition, the mobile communication terminal is provided with separate antennas or a common antenna for its standard communication and GPS communication.
FIG. 1 illustrates a structure of a conventional CDMA mobile communication terminal receiver with a GPS function. As illustrated in FIG. 1, the conventional mobile communication terminal receiver comprises a combined GPS and CDMA multiband antenna (hereinafter referred to as “GPS/CDMA antenna”) 110, a GPS/CDMA RF receiver 120 and a baseband processor 130.
Referring to FIG. 1, the GPS/CDMA antenna 110 receives a GPS RF navigation signal in a frequency band of 1575.42 MHz or 1227.6 MHz, and a CDMA RF signal in a frequency band of 900 MHz, 1.8 GHz, or 2 GHz. The RF receiver 120 converts the received GPS and CDMA RF signals into baseband signals. The baseband processor 130 extracts time and position information from the baseband GPS signal, and processes the baseband CDMA signal.
In a CDMA mobile communication system, the quality of an RF signal can vary greatly over a very short period of time depending on the propagation characteristics of an RF carrier signal, such as fading, echoes, and interference. To cope with this variation, typical mobile communication systems enable a mobile communication part (i.e., a mobile communication terminal) to obtain a diversity effect, by providing a corresponding stationary communication part (i.e., a base station) with a device for transmission and reception diversity.
However, this diversity device of the base station cannot cope with the propagation characteristics of a signal between the base station and the mobile communication terminal. Moreover, in a CDMA2000 system supporting a high data rate of 153.6 Kbps and over, the existing mobile communication terminal with a single antenna cannot sufficiently satisfy a required data rate, and a demand for an improvement in network link quality, which is required due to an increase in the number of subscribers. For the purpose of solving these problems, many techniques for obtaining a diversity effect in a mobile communication terminal have been disclosed. One of the techniques is to equip the mobile communication terminal with two antennas and two RF receivers, to receive two signals and to combine the two received signals in a baseband processor.
FIG. 2 illustrates a structure of a conventional CDMA mobile communication terminal receiver with GPS and diversity functions. As illustrated in FIG. 2, the conventional mobile communication terminal comprises a GPS antenna 210, a GPS RF receiver 220, first and second CDMA antennas 212 and 214, first and second CDMA RF receivers 222 and 224, and a baseband processor 230.
Referring to FIG. 2, the GPS antenna 210 receives a GPS RF navigation signal in a frequency band of 1575.42 MHz or 1227.6 MHz, and the GPS RF receiver 220 converts the received GPS RF navigation signal into a baseband signal. Each of the first and second CDMA antennas 212 and 214 receives a CDMA RF signal in a frequency band of 900 MHz, 1.8 GHz, or 2 GHz, and each of the first and second CDMA RF receivers 222 and 224 converts the received CDMA RF signal into a baseband signal. The baseband processor 230 extracts time and position information from the baseband GPS signal provided from the GPS RF receiver 220, and combines and processes first and second baseband CDMA signals provided from the first and second CDMA RF receivers 222 and 224.
Using the above diversity scheme with two antennas and two RF receivers, the baseband processor 230 needs a special algorithm for combining multiple baseband reception signals. In particular, this process should be performed very rapidly in the CDMA2000 system supporting a high data rate. An MRC (Maximal Ratio Combining) diversity technique, an IRC (Interference Rejection Combining) diversity technique, and many other techniques have been used as an adaptive combining diversity technique used in a mobile communication terminal demanding high-speed data processing. Referring to FIG. 2, the baseband processor 230 includes an MRC algorithm processor 232 for the adaptive combining diversity.
However, in a small-sized mobile communication terminal, even though two antennas are used for a diversity effect, it is difficult to obtain a sufficient space diversity effect. Moreover, the use of two antennas and two RF receivers in a mobile communication terminal hinders miniaturization, integration and increases the cost of the mobile communication terminal.